Pyridine dinitrogen pentoxide

The nitration reagents (NO2 Y) for electrophilic aromatic nitration span a wide range and contain anions Y such as nitric acid (Y = OH-), acetyl nitrate (Y = OAc-), dinitrogen pentoxide (Y = NO3-), nitryl chloride (Y = Cl-), TV-nitropyridinium (Y = pyridine) and tetranitromethane [Y = C(N02)3-]. All reagents contain electron-deficient species which can serve as effective electron acceptors and form electron donor-acceptor (EDA) complexes with electron-rich donors including aromatic hydrocarbons107 (ArH, equation 86). Excitation of the EDA complexes by irradiation of the charge-transfer (CT) absorption band results in full electron transfer (equation 87) to form radical ion... 

Dinitrogen pentoxide has been used for aromatic nitration in other media and some are notable. While a solution of dinitrogen pentoxide in carbon tetrachloride will not convert 1,3-dinitrobenzene to 1,3,5-trinitrobenzene, a solution in concentrated sulfuric acid at 160 °C will effect this conversion. In this medium dinitrogen pentoxide is fully ionized to nitronium and nitrate ions. Solutions of dinitrogen pentoxide in liquid sulfur trioxide have been used for the nitration of some deactivated pyridines. ... 

Benzotriazine 1,3-dioxide (2 a) was prepared in 65% yield by treating the phenyldiazene oxide 1 with nitrosyl tetrafluoroborate in acetonitrile and then with 3-chloroperoxybenzoic acid in pyridine,34 or by reacting 1 with dinitrogen pentoxide in nitromethane or dichloromethane.34 The in situ occurring reaction of 1 with nitric acid and sulfuric acid led to the isolation of the nitro derivatives 2b-d.33... 

Nitration of pyridine has been achieved using dinitrogen pentoxide -sulfur dioxide system to give 3-nitropyridine (61) (Scheme 29) <94ACS(48)181). 

With dinitrogen pentoxide pyridine gives 1-nitropyridinium nitrate sa and with nitronium fluoborate the corresponding fluoborate is formed Pyridine forms a 1 1 complex with phosphorus pentachloride Sc with sulphur dioxidei29 (43) and with sulphur trioxide o (44). The last is useful as a sulphonating agent (p. 80), and is formed from its components in carbon tetrachloride, from pyridine and fuming sulphuric acid, and from pyridine and chlorosulphonic acid. Its reactions are discussed later (p. 177). 

Dinitrogen tetroxide is less reactive than the pentoxide but more selective. Thus, although benzene is hardly attacked by pure N204, pyridine is converted by it into 3-nitropyridine in about 10% yield.134... 

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